1. Field of the Invention
The present invention relates to a hybrid system of vehicle designed to drive a generator by mechanical power of an engine and drive an electric motor by electric power generated by the generator.
2. Description of the Related Art
Heretofore, there has been known a hybrid system vehicle designed to be driven by an electric motor having a plurality of driving power sources, such as an engine, a generator and a battery, while controllably activating the driving power sources simultaneously or individually depending on conditions. For example, Japanese Patent Laid-Open Publication No. 2005-33886 discloses such a series type of hybrid system.
In a series type of hybrid system, an AC-DC inverter and a converter for voltage or frequency conversion are typically inserted between a generator/electric motor and a battery, and it is know that a relatively large electric power loss occurs during conversion processes therein.
Thus, there is the need for disusing the inverter and the converter. In reality, the series type of hybrid system includes a mode where electric power is supplied from a generator directly to an electric motor, and the disuse of the inverter and the converter without effective measures will cause difficulty in generating an output of an engine as a driving power source of the generator, fully in conformity to a required vehicle driving power determined by a depression amount of an accelerator pedal or a brake pedal operated by a driver, a vehicle speed, etc. If a desired accuracy in conformity is not ensured, overshoot (excess of generator output) or undershoot (deficiency of generator output) will occur to preclude a required driving torque from being adequately obtained.
Therefore, when the inverter and the converter are eliminated from the series type of hybrid system to suppress an electric power loss, it is necessary to accurately control an engine output as a driving power source of a generator in conformity to a required vehicle driving power without the need for correcting electric power by a battery.